[ticket/11791] Load adm/ events from styles/adm/event/

PHPBB3-11791
[ticket/11818] Update Symfony dependencies to 2.3.*

PHPBB3-11818
[prep-release-3.0.12] Bumping version number for 3.0.12-RC3.
[prep-release-3.0.12] Update Changelog for 3.0.12-RC3 release.
[ticket/11755] MySQL upgrader out of date

De-duplicating code from create_schema_files, mysql_upgrader.

New file phpbb/db/schema_data which contains all the current schema data.

New function in db_tools public static function get_dbms_type_map() to make the
type map available everywhere (without requiring $db be setup already)

PHPBB3-11755
Merge remote-tracking branch 'EXreaction/ticket/11755' into develop
Merge remote-tracking branch 'EXreaction/ticket/11818' into develop
Merge remote-tracking branch 'EXreaction/ticket/11791' into develop
Merge branch 'prep-release-3.0.12' into develop-olympus

* prep-release-3.0.12:
  [prep-release-3.0.12] Update Changelog for 3.0.12-RC3 release.
  [prep-release-3.0.12] Bumping version number for 3.0.12-RC3.

Conflicts:
	phpBB/includes/constants.php
	phpBB/install/database_update.php
	phpBB/install/schemas/schema_data.sql
Merge branch 'develop-olympus' into develop

* develop-olympus:
  [prep-release-3.0.12] Update Changelog for 3.0.12-RC3 release.
  [prep-release-3.0.12] Bumping version number for 3.0.12-RC3.

Conflicts:
	build/build.xml
	phpBB/install/database_update.php
Merge branch 'develop' of https://github.com/phpbb/phpbb3 into develop